SURGE ARRESTERS

70-139 (b) Exposed Noncurrent-Carrying Metal Parts. Exposed noncurrentcarrying metal parts of portable or mobile equipment shall be connected by an equipment grounding conductor to the point at which the system neutral impedance is grounded. (c) Ground-Fault Current. The voltage developed between the portable or mobile equipment frame and ground by the flow of maximum groundfault current shall not exceed 100 volts. (d) Ground-Fault Detection and Relaying. Ground-fault detection and relaying shall be provided to automatically deenergize any high-voltage system component that has developed a ground fault. The continuity of the equipment grounding conductor shall be continuously monitored so as to deenergize automatically the high-voltage feeder to the portable or mobile equipment upon loss of continuity of the equipment grounding conductor. (e) Isolation. The grounding electrode to which the portable or mobile equipment system neutral impedance is connected shall be isolated from and separated in the ground by at least 20 feet (6.1 m) from any other system or equipment grounding electrode, and there shall be no direct connection between the grounding electrodes, such as buried pipe, fence, etc. (f) Trailing Cable and Couplers. High-voltage trailing cable and couplers for interconnection of portable or mobile equipment shall meet the requirements of Part C of Article 400 for cables and Section 710-45 for couplers. 250-155. Grounding of Equipment. All noncurrent-carrying metal parts of fixed, portable, and mobile equipment and associated fences, housings, enclosures, and supporting structures shall be grounded. Exception No. 1: Where isolated from ground and located so as to prevent any person who can make contact with ground from contacting such metal parts when the equipment is energized. Exception No. 2: Pole-mounted distribution apparatus as provided in